We propose that breath ammonia is a surrogate measure of nitrogenous waste loading in the blood of patients suffering from End Stage Renal Disease. We present preliminary infrared spectroscopic data of human breath from a limited study of n=7 patients undergoing kidney dialysis. Breath ammonia concentration drops from approximately 2000ppb+/- 10% to approximately 200ppb+/-10% between the beginning and the end of the treatment session. We show correlations with reductions in blood urea nitrogen (BUN: approximately 90mg/dL to approximately 30mg/dL) and creatinine (approximately 14mg/dL to approximately 5mg/dL) determined by assaying blood samples taken at every breath measurement. We propose in Phase I to expand the study to n=50 patients to 1) validate the use of breath ammonia as a surrogate measure of BUN and creatinine, 2) refine breath collection and spectroscopic methods, 3) further miniaturize the spectrometer. We will use the Phase I results to design an n equal to or > 500 Phase II patient study to obtain FDA Approval of the spectrometer and to engineer the system into a package small enough to be 1) incorporated into dialysis machines for continuous in-situ assessment of dialysis efficacy and 2) used in the homes of ESRD patients and those at risk of ESRD, such as diabetics and hypertensives. PROPOSED COMMERCIAL APPLICATIONS: Provide every kidney dialysis patient and nephrologist with an instantaneous measure of the progress and efficiency of dialysis treatment. Substitute regular breath measurement for currently-used infrequent blood panels to determine when to begin and stop treatment. Integrate instrument into dialysis machines for in-situ analysis. U.S. Market: >220,000 dialysis patients treated 3 times per week corresponding to 34.32 million dialysis sessions per year Painlessly assess and screen the well-being of diabetics, hypertensives, and premature babies with potential kidney/liver trouble. U.S. Market > 2,000,000 individuals per year